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Texas Instruments SN74ALS642A-1DB
- Part No.:
- SN74ALS642A-1DB
- Manufacturer:
- Texas Instruments
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SN74ALS642A-1DB.pdf
- Description:
- BUS XCVR SINGLE 8-CH OPEN COLLEC
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Product details
Overview
SN74ALS642A-1DB from Texas Instruments is an octal inverting bidirectional bus transceiver in a 20-pin SOIC (DW) package, designed for asynchronous two-way data transfer between A and B buses with direction control via DIR and isolation via OE. It supports 5-V operation, delivers 48 mA low-level output current (IOL), and operates across 0°C to 70°C for industrial bus interface applications.
For engineers reviewing the SN74ALS642A-1DB datasheet, SN74ALS642A-1DB pinout, SN74ALS642A-1DB application, or SN74ALS642A-1DB equivalent, key selection criteria include its inverting logic function, 48 mA drive capability, 30 ns max propagation delay, 20-pin DW package footprint, and compatibility with legacy TTL/ALS bus systems requiring isolated bidirectional data routing.
Technical Context
The SN74ALS642A-1DB implements true 8-bit bidirectional data flow controlled by DIR (data direction) and OE (output enable), where DIR = L routes B→A and DIR = H routes A→B, while OE = H forces all outputs into high-impedance state. Its inverting logic means each transmitted bit is complemented during transfer.
It uses bipolar ALS (Advanced Low-Power Schottky) technology, delivering higher drive strength than standard LS while maintaining compatible voltage thresholds (VIL = 0.8 V, VIH = 2 V) and low ICC (15 mA typical at VCC = 5.5 V, outputs high). Switching performance is specified under 50 pF load and 680 Ω termination.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Function | Inverting bidirectional bus transceiver - complements data during A↔B transfer, enabling polarity-aware bus arbitration. |
| Supply Voltage (VCC) | 4.5 V to 5.5 V - compatible with standard 5-V TTL/ALS power rails; absolute max 7 V. |
| Low-Level Output Current (IOL) | 48 mA (at VCC = 4.75–5.25 V) - drives heavy capacitive loads or multiple TTL inputs without external buffers. |
| Propagation Delay (tPLH/tPHL) | 10–30 ns (A/B ↔ A/B, VCC = 4.5–5.5 V, CL = 50 pF) - ensures timing margin in 20–30 MHz bus cycles. |
| Operating Temperature | 0°C to 70°C - qualified for commercial/industrial ambient environments, not extended or automotive grade. |
| Input Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - matches standard TTL logic levels for seamless interfacing with 74LS/74ALS families. |
| Quiescent Current (ICC) | 8–15 mA (outputs high, VCC = 5.5 V) - low static power vs. AS-series alternatives, critical for dense board layouts. |
Pinout & Package
SN74ALS642A-1DB is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, 12.83 mm long, 2.65 mm max height, with 1.27 mm pitch gull-wing leads. Pin 1 is marked by a beveled corner or notch on the top surface.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Active-High signal selecting A→B (DIR = H) or B→A (DIR = L); determines data flow path through internal inverting transceivers. |
| 2 (A1) | A-Bus Data I/O | First bit of A-side 8-bit bus; functions as input when DIR selects B→A, output when DIR selects A→B; inverted at B-side. |
| 3–9 (A2–A8) | A-Bus Data I/O | Remaining 7 bits of A-side bus; identical electrical behavior to A1, supporting full octal bidirectional transfer with inversion. |
| 10 (GND) | Ground Reference | Primary signal return path; must be low-inductance connection to minimize switching noise coupling into data lines. |
| 11–18 (B1–B8) | B-Bus Data I/O | 8-bit B-side bus; receives inverted data from A when DIR = H, or drives inverted data to A when DIR = L. |
| 19 (VCC) | Power Supply | +5 V supply rail; requires local 0.1 µF ceramic decoupling adjacent to pin to suppress high-frequency transients. |
| 20 (OE) | Output Enable Input | Active-Low control: OE = L enables transceiver operation; OE = H places all A and B pins in high-Z state for bus isolation. |
Key Features
| Feature | Design Value |
|---|---|
| Inverting data path | Guarantees signal polarity inversion during A↔B transfer, enabling differential bus signaling schemes and parity generation. |
| 48 mA output drive (-1 version) | Supports direct connection to up to 12 standard TTL loads (per output), eliminating need for external line drivers in legacy backplane designs. |
| High-impedance isolation | OE-controlled 3-state outputs allow multiple transceivers to share common A/B buses without contention or signal corruption. |
| ALS process technology | Delivers 2× speed and 50% lower power vs. standard LS, with robust noise immunity (VIK = −1.5 V) for noisy industrial environments. |
| 20-pin DW package compatibility | Matches industry-standard SOIC-20 footprint (JEDEC MS-013), enabling drop-in replacement for SN74ALS641A-1DW and SN74AS641DW in existing layouts. |
Applications
| Industrial Backplane Interface | Legacy System Bus Extension |
|---|---|
|
Use Scenario: Connecting microcontroller local bus to a multi-slot ISA-style backplane with separate address/data lines. IC Role / Device Role / Timing Role: Bidirectional data transceiver isolating CPU and peripheral slots; DIR toggled per transaction phase, OE asserted during bus arbitration. Use Value: Enables reliable 8-bit data handshaking between mismatched voltage domains using only one device per bus segment, reducing component count vs. discrete buffer solutions. |
Use Scenario: Extending a vintage 8086/8088 system's data bus to add memory-mapped I/O cards without modifying motherboard traces. IC Role / Device Role / Timing Role: Inverting transceiver bridging motherboard D0–D7 to expansion slot D0–D7; DIR tied to CPU DT/R̅, OE driven by IO/M̅ and RD̅/WR̅. Use Value: Preserves signal integrity over 15 cm traces while meeting strict 8086 setup/hold timing due to sub-30 ns propagation delays. |
| Test Equipment Data Routing | Programmable Logic Interfacing |
|
Use Scenario: Routing stimulus/response signals between FPGA-based pattern generator and DUT in automated test fixtures. IC Role / Device Role / Timing Role: Direction-controlled bus switch allowing FPGA to drive DUT inputs or capture DUT outputs on same physical lines. Use Value: Eliminates need for dual 8-bit unidirectional buffers and reduces fixture PCB layer count by consolidating A/B paths into single 20-pin IC. |
Use Scenario: Interfacing CPLD configuration data bus to external PROM or flash memory with shared address/data lines. IC Role / Device Role / Timing Role: Isolating CPLD I/O pins from memory bus during configuration; DIR set by CPLD control logic, OE synchronized to memory access strobes. Use Value: Prevents bus contention during CPLD reconfiguration while maintaining full 8-bit throughput for fast memory read/write cycles. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar bidirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS641A-1DW | True (non-inverting) logic function; otherwise identical pinout, timing, and drive specs. | Used where bus polarity must be preserved (e.g., direct memory data mirroring), not where inversion aids protocol encoding. | Select SN74ALS641A-1DW when system-level logic requires non-inverted data transfer; verify DIR/OE control timing remains compatible. |
| SN74AS641DW | Faster propagation (7.5 ns max tPHL), higher IOL (64 mA), but 2× higher ICC (82 mA typ) and no -1 variant for 48 mA spec. | Suitable for high-speed backplanes (>25 MHz) where power budget allows; less ideal for thermally constrained or battery-backed modules. | Choose SN74AS641DW only if timing margin is insufficient with ALS family; confirm thermal design accommodates doubled quiescent power. |
Compared with SN74ALS642A-1DB, SN74ALS641A-1DW provides identical drive and packaging but preserves signal polarity, while SN74AS641DW trades higher power for faster switching-making the SN74ALS642A-1DB optimal for cost-sensitive, thermally constrained 5-V industrial bus interfaces requiring inversion.
Availability
SN74ALS642A-1DB is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, test equipment data routing, and programmable logic interfacing requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS642A-1DB includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Texas Instruments is a global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74ALS642A-1DB belongs to TI's legacy 74ALS logic family, engineered for high-reliability, low-power 5-V bus interfacing in industrial control systems and retro-computing infrastructure where compatibility with TTL-era designs is essential.
FAQ
What logic function does the SN74ALS642A-1DB implement?
The SN74ALS642A-1DB implements an inverting bidirectional bus transceiver function: data transferred from A to B or B to A is logically complemented. This is confirmed in the device function table and logic diagrams of the SDAS300 datasheet, distinguishing it from the true-function SN74ALS641A-1DB. The inversion occurs regardless of direction, making SN74ALS642A-1DB suitable for applications requiring polarity transformation during bus bridging.
What is the maximum output drive capability of the SN74ALS642A-1DB?
The SN74ALS642A-1DB supports a maximum low-level output current (IOL) of 48 mA per pin when VCC is between 4.75 V and 5.25 V, as specified in the "recommended operating conditions" table of the SDAS300 datasheet. This enhanced drive-relative to the standard SN74ALS642A-is the defining feature of the "-1" suffix and enables direct driving of heavier bus loads without external buffers.
Which package types are available for the SN74ALS642A-1DB?
The SN74ALS642A-1DB is available exclusively in the SOIC (DW) package, as confirmed by TI's Package Option Addendum showing active orderable part numbers SN74ALS642A-1DW and SN74ALS642A-1DW.A. While other variants like SN74ALS642A-1N (PDIP) exist, the "DB" suffix specifically denotes the DW (SOIC) variant per TI's standard naming convention and packaging documentation.
Does the SN74ALS642A-1DB support 3.3-V operation?
No, the SN74ALS642A-1DB is rated only for 4.5 V to 5.5 V supply operation, with absolute maximum VCC of 7 V. Its input thresholds (VIL = 0.8 V, VIH = 2.0 V) and output voltage specs (VOH = 5.5 V) are defined for 5-V systems. Operating at 3.3 V violates recommended conditions and risks unreliable logic levels or excessive ICC; use 74LVC or 74ALVC series for 3.3-V compatibility.
How does the SN74ALS642A-1DB handle bus isolation?
The SN74ALS642A-1DB achieves bus isolation via its active-low Output Enable (OE) input: when OE is high, all A and B port pins enter a high-impedance (3-state) condition, electrically disconnecting both buses. This is verified in the function table (OE = H → Isolation) and electrical characteristics (off-state leakage < ±0.1 mA). Isolation is independent of DIR state, allowing safe bus sharing among multiple transceivers.
SN74ALS642A-1DB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
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- Number of Elements:
- -
- Number of Bits per Element:
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- Input Type:
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- Output Type:
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- Current - Output High, Low:
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- Voltage - Supply:
- -
- Operating Temperature:
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- Grade:
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- Qualification:
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- Mounting Type:
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- Supplier Device Package:
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SN74ALS642A-1DB FAQ
1.How can I place an order for SN74ALS642A-1DB through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS642A-1DB on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for SN74ALS642A-1DB reliable?
The price and inventory of SN74ALS642A-1DB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS642A-1DB is usually 5 days.
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Once your SN74ALS642A-1DB order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for SN74ALS642A-1DB?
For technical support, including SN74ALS642A-1DB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS642A-1DB requirements.
6.How does Aetrix verify that SN74ALS642A-1DB is sourced from the original manufacturer or authorized distributors?
All SN74ALS642A-1DB products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74ALS642A-1DB meets industry standards.
7.What is the process for return or replacement of SN74ALS642A-1DB?
All SN74ALS642A-1DB units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS642A-1DB, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The SN74ALS642A-1DB part is unused and in its original packaging.
Return procedure for SN74ALS642A-1DB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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